This invention resulted from a contract made by the United States Department of Energy and relates to a nuclear reactor control apparatus and, more particularly, to an apparatus for quickly releasing a shaft carrying a neutron-absorbing material that is inserted into a nuclear reactor core to control fission therein.
Complete shutdown of the operation of a nuclear reactor, commonly referred to as a scram, is required under any condition wherein continued operation could damage the reactor. A scram is generally effected by releasing a vertically disposed control rod carrying a neutron-absorbing material at its lower end, thus allowing the rod to drop to a level wherein it positions the absorber material within the reactor core and thereby stops fission therein. It is obviously important that components for releasably gripping such rods must have a high operational dependability. If a control rod release mechanism is operated by fluid pressure, it is also desirable to use a design that operates in a fail-safe mode by releasing the control rod in the event of loss of pressure.
The inertia of long safety rods limits the speed at which the control rods can be moved to scram position. Furthermore, it is possible that seismic shocks can interfere with the release of absorber carrying rods by bending them so that they cannot slide in their bearings. All scram control mechanisms must, of course, provide a means for returning safety rods to their raised position when an adverse operating condition has been eliminated.
As shown in the description of scram mechanisms presented in the text titled "Fast Reactor Technology: Plant Design", published by M.I.T. Press in 1966, electromagnets have previously been used to hold reactor safety rods in a raised position until an unsafe reactor operating condition occurs, at which time the electromagnets are deenergized to release the rods. An electromagnet is incorporated in a latch mechanism of one embodiment of the invention disclosed herein, but the construction of safety rod release apparatus in accordance with the invention differs from that of known devices. Furthermore, known safety rod release devices use only one release means, whereas in a preferred embodiment of this invention a plurality of release latches provide for two types of scram.